1. Technical Field
The present invention generally relates to a visual telephone system, and more particularly relates to a visual telephone system connected to a telephone line for controlling the use of such a telephone line connected to a telephone switching network.
2. Related Art
Generally, there may be connected a number of telephone sets to a single telephone network line which has a specific call number.
Visual telephones may be connected to such a signal transmission line (i.e., a telephone network line) so as to transmit and receive audio (i.e., voice) and visual (i.e., video) information to/from another visual telephone via the telephone network line. If the communication between calling and called visual telephones over the telephone network line is achieved, audio communication is possible, but visual communication is impossible. This is because audio and visual signals must be simultaneously transmitted and received between the calling and called visual telephones. Thus, in order to transmit and receive the audio signal simultaneously with the visual signal via a telephone network line, each visual telephone must include a modem device for converting analog information which contain audio and visual signals into digital information.
During the visual communication of a calling visual telephone with a called visual telephone via a telephone network line therebetween, when another visual or audio telephone connected with the telephone network line is off-hooked by a caller, the visual communication is stopped because noise is introduced into the telephone network line. In order to solve the problem an, LED (light emitting diode) is installed on a body of a visual telephone connected to a telephone network so as to indicate whether or not another visual telephone is being connected to the telephone network line. However, even when the LED installed on the visual telephone is turned on, another visual telephone which is commonly connected with the telephone network line may be involuntarily off-hooked by a caller, such that the visual communication of the visual telephone with another visual telephone is stopped because of noise introduction as described above.